I only have a 12 inch skillet. so should i skip it?
Not necessarily...a 9-inch skillet has a surface area of approximately 63.6 inches, while a 12 inch skillet has a surface area of 113.4 inches. Given that the surface area of your skillet is nearly double that of the intended skillet size, you should double the recipe to achieve similar results. You'll also need to bake it for longer. Totally do-able, but just more effort.
I bet you could also make it in a regular 9 inch cake pan using Maida Heatter's technique of melting butter in the cake pan while the oven heats up, spreading it around, and then pouring your batter into the hot buttered pan. (I don't have a 9 inch skillet either, but I may try this with some very ripe bananas that I need to do something with--thanks for pointing it out!)
drbabs and littleknitter both offer great advice. Plus mrslarkin had good luck making it in a 9-inch cake pan so if you have one of those, go for it. Or even a loaf pan. Hope you like it!
I only have a 12 inch cast iron pan too. I used an 8.5/9 inch cake pan to make this. Came out really good. Can't remember how long I cooked it for. Sorry.
I should've mentioned yesterday that I used a skillet to get a crunchier exterior. If you use a loaf pan you should increase the baking time to about an hour, but you probably already knew that.